1. Technical Field
The present invention relates to a semiconductor device having a junction of an electrode pad with a bonding wire of a semiconductor chip, which is encapsulated with an encapsulating resin.
2. Related Art
Typical conventional semiconductor devices having an electrode pad and a lead frame on a semiconductor chip, which are connected via wire bonding and encapsulated with an encapsulating resin, are described in Japanese Patent Laid-Open No. H10-303,239 (1998) and Japanese Patent Laid-Open No. H04-206,651 (1992).
Japanese Patent Laid-Open No. H10-303,239 describes that a gold (Au) alloy containing manganese (Mn) as an essential component is employed for forming a bonding wire, and an encapsulating resin containing bromine (Br) or antimony (Sb) is employed. Further, Japanese Patent Laid-Open No. H10-303,239 describes the following aspects. In order to enhance fire retardancy, the encapsulating resin should essentially contain at least one of bromine and antimony, and therefore sufficient encapsulating fire retardant effect can not be obtained if the concentration thereof is less than 0.1% wt. A use of a thin wire of gold alloy essentially containing Mn can enhance fire retardancy without deteriorating reliability, even if contents of bromine and antimony is increased as compared with conventional formulation. Although it is found that an addition of single palladium (Pd) allows decreasing a growing rate of a compound phase, the inhibition effect for a corrosion is not sufficient. In particular, in order to obtain sufficient effect of delaying a corrosion in a long time-heating process that provides a condition of a corrosion corresponding to a status, in which a corrosion extensively proceeds over the compounds, it is necessary to select an addition of Pd of greater than about 1% wt. However, an inclusion of Pd at higher concentration causes problems, in which a flat geometry of a ball junction may be formed, or a silicon substrate is damaged during a formation of a junction due to a hardening of the ball junction. Although decreased quantity of additional Pd can provide acceptable geometry of the ball junction, a problem of a reduced inhibition for the corrosion is caused after the compound is sufficiently grown in the junction by heating for longer time. An increase of electric resistance, which has been otherwise difficult to be inhibited by adding Pd alone, can be sufficiently inhibited by jointly adding manganese (Mn), and therefore even a smaller quantity of Pd can considerably enhance the effect for inhibiting a progress of the corrosion. For these reasons, combined use of Mn and Pd is effective for inhibiting the progress of the corrosion in both shorter and longer term.
On the other hand, Japanese Patent Laid-Open No. H04-206,651 describes a semiconductor device obtained by: producing a structure by mounting a semiconductor chip on a die pad of a lead frame and forming an electrical connecting with a bonding pad via a bonding wire; coating the obtained structure with a protective layer that includes no fire retardant agent or no fire retardant auxiliary agent; and coating the circumference thereof with a fire retardant resin.